This invention relates to a squeeze film shaft damper for rotating machines such as hot gas turbine engines, and more particularly, to damping fluid pressure control in such dampers.
Squeeze film shaft dampers permit a shaft and an associated bearing to have some limited radial movement in a bearing housing where a thin annular squeeze film space is defined between a circumferential bearing member, usually the annular outer race of a rolling element bearing, and an opposite circumferential wall of an annular chamber in the bearing housing in which the bearing race is housed. A damper fluid, usually an oil, is introduced into the annular squeeze film space to generate a resistance to radial motion of the shaft and its associated bearing in the bearing housing chamber. An imbalance in the gas turbine rotor-shaft assembly, for example, may cause the rotor shaft to undergo limited orbital motion which is transmitted to its supporting bearing to cause the outer race of the bearing to undergo orbiting motion in its housing chamber. This orbiting motion generates a very high fluid pressure wave moving circumferentially in the described annular squeeze film space which provides fluid resistance to further shaft radial and orbital motion. Damping action in a damper causes a significant temperature rise in the damper fluid, and heat is dissipated from the damper by means of continuous recirculation of oil to and from the squeeze film space. It is important in effective damper operation to control and maintain the described circumferentially moving pressure wave while at the same time recirculating oil through the damper without deleteriously affecting the pressure wave.